Despite the maximized metal dispersion offered by single-atom catalysts, further improvement of intrinsic activity can be hindered by the lack of neighboring metal atoms in these systems. Here we report the use of isolated Pt₁ atoms on ceria as “seeds” to develop a Pt-O-Pt ensemble, which is well-represented by a Pt₈O₁₄ model cluster that retains 100% metal dispersion. The Pt atom in the ensemble is 100–1000 times more active than their single-atom Pt₁/CeO₂ parent in catalyzing the low-temperature CO oxidation under oxygen-rich conditions. Rather than the Pt-O-Ce interfacial catalysis, the stable catalytic unit is the Pt-O-Pt site itself without participation of oxygen from the 10–30 nm-size ceria support. Similar Pt-O-Pt sites can be built on various ceria and even alumina, distinguishable by facile activation of oxygen through the paired Pt-O-Pt atoms. Extending this design to other reaction systems is a likely outcome of the findings reported here.

Four Cu/SAPO-34 catalysts are used to research the effect of their acid content on their NH₃-SCR activity, by changing the proportion of Si in the catalyst. Though the catalysts exhibit similar Cu loading performed by an ion-exchange method, they lead to different NO conversions in the temperature range of 120–600 °C. The NH₃-TPD results show that varying the proportion of Si can adjust the acid content of SAPO-34. In the low temperature range, kinetic tests prove that the various acid contents did not affect the apparent activation energy (E_a) of the Selective Catalytic Reduction by NH₃ (NH₃-SCR) over Cu/SAPO-34. But it is found that the acid densities are related to the NO conversion at low temperature. In the high temperature range, increasing the acid content of the Cu/SAPO-34 catalysts inhibits the observed NH₃ conversions in the NH₃ oxidation results. As NH₃ oxidation and NH₃-SCR are competing reactions and the former can decrease NO conversion, this inhibition is therefore beneficial to NH₃-SCR. Finally, the influence of the acid content of the catalysts on the NH₃ oxidation is also investigated by kinetic tests.